Cathode material for lithium-sulfur batteries and lithium-sulfur batteries containing the same

Abstract

To provide a carbon composite used for a positive electrode of a lithium sulfur battery, and a manufacturing method therefor.SOLUTION: A carbon composite contains: a porous carbon material in which at least one sulfur is doped; and at least one catalyst containing a transition metal. The catalyst is positioned at at least one of an external front surface of the porous carbon material in which the at least one sulfur is doped and an internal front surface of a pore.SELECTED DRAWING: Figure 2a

Description

Technical Field

[0001] The present invention relates to a positive electrode material for a lithium-sulfur battery and a lithium-sulfur battery including the same.

[0002] This application claims priority based on Korean Application No. 2022-0044174 filed on April 8, 2022, and Korean Application No. 2022-0140744 filed on October 27, 2022, and all the contents disclosed in the specification of the applications are incorporated herein.

Background Art

[0003] A lithium-sulfur battery is a battery system that uses a sulfur-based material having an S-S bond (sulfur-sulfur bond) as a positive electrode active material and lithium metal as a negative electrode active material. Sulfur, which is the main material of the positive electrode active material, has advantages such as abundant global resources, no toxicity, and low weight per atom. [[ID=]17]

[0004] As the application areas of secondary batteries expand to electric vehicles (EVs) and energy storage systems (ESSs), etc., compared to lithium-ion secondary batteries having a relatively low energy storage density (~250 Wh / kg) with respect to weight, lithium-sulfur battery technology that can theoretically achieve a high energy storage density (~2,600 Wh / kg) with respect to weight has been in the spotlight.

[0005] In a lithium-sulfur battery, during discharge, lithium, the negative electrode active material, is oxidized while releasing electrons and ionizing into lithium cations, and the sulfur-based material, the positive electrode active material, is reduced while accepting electrons. Here, the reduction reaction of the sulfur-based material causes the SS bond to accept two electrons and is converted into a sulfur anion. The lithium cations generated by the oxidation reaction of lithium are transferred to the positive electrode through the electrolyte, and these combine with sulfur anions generated by the reduction reaction of the sulfur-based compound to form a salt. Specifically, the sulfur before discharge has a cyclic S8 structure, which is reduced to lithium polysulfide (Li2S) x It is converted to ) and completely reduced to produce lithium sulfide (Li2S).

[0006] Thus, since sulfur used as a positive electrode active material is an insulator, the movement of electrons generated by electrochemical reactions is difficult, and polysulfide (LiS) generated during the charging and discharging process is not easily formed. x There were problems with leaching and slow kinetic activity due to the electrochemical reaction caused by the low electrical conductivity of sulfur and lithium sulfide, which reduced battery life characteristics and speed characteristics.

[0007] In connection with this, research is currently underway to improve the performance of lithium-sulfur secondary batteries by using platinum (Pt), which is widely used as an electrochemical catalyst, to enhance the kinetic activity of the sulfur oxidation-reduction reaction during the charging and discharging process of lithium-sulfur secondary batteries. However, precious metal catalysts such as platinum are expensive and therefore difficult to commercialize. Furthermore, there is a risk of poisoning due to the sulfur oxidation-reduction reaction during the charging and discharging process, making it difficult to utilize them as cathode materials for lithium-sulfur secondary batteries.

[0008] Furthermore, research is underway on single-atom catalysts to improve the performance of lithium-sulfur secondary batteries by increasing atomic utilization efficiency to near 100% and minimizing the catalyst content inside the cathode. However, most single-atom catalysts have low adsorption rates to lithium sulfide, resulting in poor conversion performance, and their effectiveness in improving the performance of lithium-sulfur secondary batteries remains insufficient. Consequently, research has also progressed on using single-atom catalysts in combination with particle-type catalysts, but this approach is ineffective because it again reduces atomic utilization efficiency.

[0009] Therefore, there is a continued need for technological development of cathode materials that can improve the kinetic activity of the electrochemical reaction during charging and discharging of lithium-sulfur secondary batteries, while simultaneously being cost-effective for commercialization. [Overview of the project] [Problems that the invention aims to solve]

[0010] Therefore, the problem that the present invention aims to solve is to provide a cathode material that solves the aforementioned problems, has excellent adsorption capacity with lithium polysulfide, and enhances the kinetic activity of sulfur oxidation / reduction reactions.

[0011] The goal is to provide a high-performance lithium-sulfur secondary battery. [Means for solving the problem]

[0012] To solve the above problems, according to one aspect of the present invention, a carbon composite in the following form is provided.

[0013] The carbon composite according to the first embodiment is The invention comprises a porous carbon material doped with at least one sulfur, and at least one catalyst comprising one or more transition metals, wherein the catalyst is located on at least one of the outer surface and the inner surface of the pores of the porous carbon material doped with at least one sulfur.

[0014] According to the second aspect, in the first aspect, The nearest neighbor interatomic distance between the transition metal contained in the catalyst and at least one sulfur doped into the porous carbon material may be 10 nm or less.

[0015] According to the third aspect, in the first or second aspect, The nearest neighbor interatomic distance between the transition metal contained in the catalyst and at least one sulfur doped into the porous carbon material may be 2 nm or less.

[0016] According to the fourth aspect, in any one aspect of the first to third aspects, The carbon composite is 200m 2 It may have a BET specific surface area of ​​1 / g or more.

[0017] According to the fifth aspect, in any one aspect of the first to fourth aspects, The catalyst may further comprise the transition metal and at least one nonmetallic element that forms a ligand with the transition metal.

[0018] According to the sixth aspect, in any one aspect of the first to fifth aspects, The catalyst may further include the transition metal, at least one nonmetallic element that forms a ligand with the transition metal, and an organic support.

[0019] According to the seventh aspect, in any one aspect of the first to sixth aspects, The catalyst may include a single atom catalyst containing one or more transition metals, wherein the one or more transition metals may be dispersed in the carbon composite at a single-atom size.

[0020] According to the eighth aspect, in any one aspect of the first to seventh aspects, The catalyst does not necessarily have to contain metallic bonds between two or more transition metals.

[0021] According to the ninth aspect, in any one aspect of the first to eighth aspects, The catalyst comprises particles containing one or more transition metals, and the average diameter of the particles (D 50 The diameter of the transition metal can be 1 to 30 nm, which is the diameter of a single atom constituting the transition metal.

[0022] According to the tenth aspect, in any one aspect of the first to ninth aspects, The catalyst comprises particles containing one or more transition metals, and the average diameter of the particles (D 50 The diameter of the single atom constituting the transition metal can be 1 to 5 times the diameter of the single atom constituting the transition metal.

[0023] According to the 11th aspect, in any one aspect of the 1st to 10th aspects, The transition metals may include zinc (Zn), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), rubidium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), cadmium (Cd), lanthanum (La), hafnium (Hf), tantalum (Ta), tungsten (W), osmium (Os), iridium (Ir), cerium (Ce), galadium (Gd), scandium (Sc), titanium (Ti), gallium (Ga), indium (In), or two or more of these.

[0024] According to the 12th aspect, in any one aspect from the 1st to the 11th aspects, The transition metal may include iron (Fe).

[0025] According to the 13th aspect, in any one aspect from the 1st to the 12th aspects, The transition metal includes iron (Fe), and the diameter (D) of the iron contained in the carbon composite. 50 ) can be 0.3nm to 5nm.

[0026] According to the 14th aspect, in any one aspect of the 1st to 13th aspects, The molar ratio of sulfur doped into the porous carbon material to one or more transition metals contained in the catalyst can be 0.5 to 8.

[0027] According to the 15th aspect, in any one aspect of the 1st to 14th aspects, The at least one sulfur may be doped in the form of a sulfur atom or a sulfur compound.

[0028] According to the 16th aspect, in any one aspect of the 1st to 15th aspects, The porous carbon material doped with at least one sulfur contains in its structure at least one of a first structure according to the following formula 1 and a second structure according to the following formula 2, wherein the ratio of the first structure to the second structure may be 1 or less in molar ratio of the first structure to the second structure.

[0029] [Formula 1] -C-SO2-C- [Formula 2] -CSC-

[0030] According to the 17th aspect, in the 16th aspect, The molar ratio of the first structure to the second structure can be 0.1 to 0.7.

[0031] According to the 18th aspect, in any one aspect from the 1st to the 17th aspects, When N(nano) is the number of pores with a diameter of less than 10 nm among all the pores of the carbon composite, and N(macro) is the number of pores with a diameter of 10 nm or more, the ratio of N(macro) to N(nano) [N(macro) / N(nano)] may be 1 or more.

[0032] According to the 19th aspect, in any one of the 1st to 18th aspects, the Raman peak intensity ratio (I G / I D ratio) of the porous carbon material may be 1 or less.

[0033] According to another aspect of the present invention, a method for producing a carbon composite of the following aspect is provided.

[0034] The method for producing a carbon composite according to the 20th aspect is (S1) a step of doping at least one sulfur in a porous carbon material; and (S2) a step of impregnating the result of the step (S1) into a transition metal-containing precursor solution and then removing the solvent, and the step (S1) includes a step of heat-treating in a state where a sulfur doping precursor and the porous carbon material are in contact. <000​​​​​​​​​​​​​​​​According to the 23rd aspect, in any one aspect of the 20th to 22nd aspects, The transition metal-containing precursor solution in step (S2) may include an organic solvent, a precursor compound of a nonmetallic element, and a precursor compound of a transition metal.

[0038] According to yet another aspect of the present invention, a positive electrode active material, a positive electrode, a lithium sulfur battery, and a battery are provided in the following embodiments.

[0039] According to the 24th aspect, A positive electrode active material is provided, comprising a carbon composite according to any one of the first to nineteen embodiments and a sulfur-based compound.

[0040] According to the 25th aspect, A positive electrode containing a positive electrode active material according to a 24th aspect is provided.

[0041] According to the 26th aspect, A lithium sulfur battery is provided, comprising a positive electrode, a negative electrode, a separation membrane interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode is a positive electrode according to the 25th embodiment.

[0042] According to the 27th aspect, A positive electrode is provided comprising a positive electrode active material containing a sulfur-based compound and a carbon composite according to any one of the first to 19 embodiments.

[0043] According to the 28th aspect, A lithium sulfur battery is provided, comprising a positive electrode, a negative electrode, a separation membrane interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode is a positive electrode according to the 27th embodiment.

[0044] According to the 29th aspect, A battery is provided which includes a positive electrode, a negative electrode, a separation membrane interposed between the positive electrode and the negative electrode, and an electrolyte, wherein at least one of the electrodes of the positive electrode and the negative electrode includes a carbon composite according to any one of the first to nineteen embodiments. [Effects of the Invention]

[0045] A carbon composite according to one aspect of the present invention is lithium polysulfide (LiPS, Li2S x It exhibits excellent adsorption properties with (2≦x≦8). Moreover, the carbon composite has properties that are advantageous for ion transfer and electron transfer, which are essential for the conversion reaction of lithium polysulfide.

[0046] Furthermore, the carbon composite has the effect of providing excellent kinetic activity in sulfur oxidation / reduction reactions.

[0047] Furthermore, the carbon composite has the effect of improving the atom utilization rate as a catalyst.

[0048] As a result, lithium-sulfur secondary batteries using the carbon composite as a support for the positive electrode additive and / or positive electrode active material have the effect of suppressing the elution of lithium polysulfide into the electrolyte and improving the sulfur conversion rate, thereby achieving stable and high performance.

[0049] In particular, a lithium-sulfur battery according to one aspect of the present invention has excellent effects in terms of initial capacity, capacity retention rate through charge-discharge cycles, and energy density of the battery.

[0050] The drawings accompanying this specification illustrate preferred embodiments of the present invention and are intended to further illustrate the technical idea of ​​the invention along with the content of the invention; therefore, the present invention shall not be construed as being limited only to what is shown in the drawings. [Brief explanation of the drawing]

[0051] [Figure 1] This diagram illustrates various functions demonstrating that a carbon composite according to one aspect of the present invention functions as an electrochemical catalyst at the positive electrode during charging and discharging of a lithium-sulfur secondary battery. [Figure 2a] This is a schematic diagram illustrating the manufacturing sequence of a carbon composite and a positive electrode using the same according to one aspect of the present invention. [Figure 2b]This graph shows the 2p spectrum of the sulfur atom (S) in the carbon composite of Example 1 of this specification, obtained by XPS analysis. [Figure 2c] This graph shows the 2p spectrum of the sulfur atom (S) in the carbon composite of Example 2 of this specification, obtained by XPS analysis. [Figure 2d] This graph shows the measurement results of the Fe element content and -SO2 / -S ratio in Comparative Example 1 (FeNC), Example 1 (FeNC-EEB-1), and Example 2 (FeNC-EEB-2) as described herein, obtained by ICP-AES analysis. [Figure 3] This image shows the results of the analysis of the distribution of Fe, O, N, C, and S in Example 1 (FeNC-EEB-1) and Example 2 (FeNC-EEB-2) of this specification, obtained by EDS analysis. [Figure 4] These images, obtained by SEM (left) and TEM (right), show the shapes of Comparative Example 1 (FeNC), Example 1 (FeNC-EEB-1), and Example 2 (FeNC-EEB-2) as described herein. [Figure 5] This graph shows the pore diameter and relative pressure results for Comparative Example 1 (FeNC), Example 1 (FeNC-EEB-1), and Example 2 (FeNC-EEB-2) as defined herein, obtained by nitrogen physicoadsorption analysis. [Figure 6] These are images showing the shapes of Comparative Example 1 (FeNC), Example 1 (FeNC-EEB-1), and Example 2 (FeNC-EEB-2) as obtained by STEM. [Figure 7] This graph shows the results obtained by FT-EXAFS for Comparative Example 1 (FeNC), Example 1 (FeNC-EEB-1), Example 2 (FeNC-EEB-2) as described herein, and for confirming the bonding of Fe elements in Fe foil. [Figure 8] This graph shows the measurement results of Fe K-edge XANES for Comparative Example 1 (FeNC), Example 1 (FeNC-EEB-1), and Example 2 (FeNC-EEB-2) as described herein. [Figure 9a]This graph shows the Tafel plots obtained by measuring the current / voltage at the positive electrode (cathode) and negative electrode (anode) during operation of Comparative Example 2 (FeNC), Example 3 (FeNC-EEB-1), and Example 4 (FeNC-EEB-2), which are lithium-sulfur coin-type batteries according to this specification. [Figure 9b] This graph shows the results of constant voltage (2.05V) discharge driving for Comparative Example 2 (FeNC), Example 3 (FeNC-EEB-1), and Example 4 (FeNC-EEB-2) as described herein. [Figure 9c] This graph shows the results of constant voltage (2.35V) charging operation for Comparative Example 2 (FeNC), Example 3 (FeNC-EEB-1), and Example 4 (FeNC-EEB-2) as described herein. [Figure 10] This graph shows the evaluation results of the charge and discharge performance of Comparative Example 2 (FeNC), Example 3 (FeNC-EEB-1), and Example 4 (FeNC-EEB-2) as described herein. [Figure 11] This graph shows the results of evaluating the operation of Comparative Example 2 (FeNC), Example 3 (FeNC-EEB-1), and Example 4 (FeNC-EEB-2) in this specification over 200 charge-discharge cycles. [Figure 12] This graph shows the results of evaluating the operation of 100 charge-discharge cycles after changing the sulfur loading amount and E / S ratio in Example 3 (FeNC-EEB-1) of this specification. [Figure 13] This graph shows the results of evaluating the charge and discharge performance of Comparative Example 3 and Example 5 in this specification. [Modes for carrying out the invention]

[0052] The present invention will be described in detail below. However, it is not limited to the following, and each component can be modified or selectively mixed as needed. Therefore, it is understood that the present invention includes all modifications, equivalents, and substitutions that fall within the concept and technical scope.

[0053] In this specification, when a configuration is said to "include" a certain component, unless otherwise specified, this does not mean that other components are excluded, but rather that other components may be included.

[0054] In this specification, the phrase "A and / or B" means "A or B or both of these."

[0055] The specific terms used herein are for convenience only and are not limiting. For example, terms indicating position, such as “up,” “down,” “left,” “right,” “front,” “back,” “inside,” and “outside,” do not indicate absolute positions but are used to indicate the relative positions or directions between components, or to indicate positions or directions in referenced drawings. The terms include not only these terms themselves, but also words containing them, their derivatives, and words with similar meanings.

[0056] According to one aspect of the present invention, a carbon composite that can be used as an electrochemical catalyst in the positive electrode of a lithium-sulfur secondary battery is provided.

[0057] Figure 1 schematically illustrates various functions demonstrating that the carbon composite according to the present invention functions as an electrochemical catalyst at the positive electrode during charging and discharging of a lithium-sulfur secondary battery. Referring to Figure 1, since the carbon composite is used as an electrochemical catalyst at the positive electrode, lithium polysulfide (Li2S x or LiS x - It can adsorb (x=8, 6, 4, 2) and suppress its elution into the electrolyte. Furthermore, it exhibits activity in the conversion reaction between lithium polysulfides, inducing rapid conversion and preventing the release of lithium sulfide (Li2S).

[0058] A carbon composite according to one aspect of the present invention comprises a porous carbon material doped with at least one sulfur, and at least one catalyst comprising one or more transition metals, wherein the catalyst is located on at least one of the outer surface and the inner surface of the pores of the sulfur-doped porous carbon material.

[0059] In one embodiment of the present invention, the catalyst containing the transition metal may be chemically and / or physically bonded to at least one of the external surface and the internal surface of the pores of the sulfur-doped porous carbon material.

[0060] In one embodiment of the present invention, the catalyst may be physically adsorbed on the outer surface and / or the inner surface of the pores of the porous carbon material, and / or may be chemically bonded by covalent bonds between the elements contained in the catalyst and the carbon of the porous carbon material.

[0061] The carbon composite of the present invention has at least one sulfur atom located in close proximity to the catalyst present on the outer surface and / or inside the pores of the porous carbon material. In this specification, the "close proximity" position is defined as a position where the nearest neighbor interatomic distance between the catalyst and the at least one sulfur atom doped into the porous carbon material is 10 nm or less.

[0062] In this specification, the nearest neighbor distance refers to the distance between the centers of the two closest atoms. The nearest neighbor distance can represent a value measured according to a known method for measuring interatomic distances, and is not limited to such a method. For example, the nearest neighbor distance can be measured using a transmission electron microscope (TEM), an atomic force microscope (AFM), a field emission electron microscope (FE-SEM), or a laser diffraction method.

[0063] In one embodiment of the present invention, the nearest neighbor interatomic distance between the catalyst and at least one sulfur doped into the porous carbon material may be 10 nm or less, specifically 5 nm or less, more specifically 2 nm or less, for example, 1.5 nm or less or 1 nm or less.

[0064] For example, the nearest neighbor interatomic distance between the catalyst and at least one sulfur doped into the porous carbon material can represent the nearest neighbor interatomic distance between the transition metal element contained in the catalyst and at least one sulfur doped into the porous carbon material.

[0065] In the carbon composite, the sulfur-doped positions can act as electron-exchangeable binding (EEB) sites. Furthermore, the sulfur can adjust the orbital level of the transition metal in the catalyst via electron exchange. For example, if the catalyst contains iron (Fe) as the transition metal, the sulfur can adjust the orbital level of iron via electron exchange. This allows the carbon composite to enhance the kinetic activity of the lithium polysulfide reduction reaction, but the mechanism of the present invention is not limited thereto.

[0066] In the present invention, the catalyst containing the transition metal can be used alone as a catalyst in the positive electrode of a lithium-sulfur battery to impart activity to the reduction reaction of lithium polysulfide. However, according to the present invention, by positioning such a catalyst on the outer surface and / or inner surface of the pores of the porous carbon material doped with at least one sulfur, the adsorption of lithium polysulfide and the activation of the sulfur oxidation / reduction reaction can be further improved.

[0067] In one embodiment of the present invention, the catalyst may contain a transition metal as an active component of the catalyst and may be any catalyst that can mediate the oxidation / reduction reaction of sulfur, without limitation.

[0068] In another aspect of the present invention, the catalyst may further comprise the transition metal and at least one nonmetallic element that forms a ligand with the transition metal. In this case, the transition metal and / or nonmetallic element present in the catalyst may be physically adsorbed and / or chemically bonded to the carbon of the porous carbon material.

[0069] In yet another embodiment of the present invention, the catalyst may further comprise the transition metal, at least one nonmetallic element that forms a ligand with the transition metal, and an organic support. When the catalyst further comprises an organic support for supporting the transition metal and the nonmetallic element, the dispersibility of the transition metal can be improved, thereby enhancing the catalytic utilization rate of the carbon composite according to one aspect of the present invention.

[0070] In yet another aspect of the present invention, the catalyst comprises an organic support, a transition metal, and at least one nonmetallic element that forms a ligand with the transition metal, wherein the catalyst may include bonding between carbon in the organic support and the transition metal, bonding between the carbon and the nonmetallic element, and bonding between the transition metal and the nonmetallic element.

[0071] In one embodiment of the present invention, the catalyst may include transition metals in the form of metal particles formed by bonding between transition metal atoms, but from the viewpoint of the atom utilization rate of the catalyst, it is preferable to include transition metals that exist as single atoms without being bonded between transition metal atoms.

[0072] Accordingly, according to one aspect of the present invention, the catalyst may include a monatomic catalyst containing one or more transition metals. As a result, the one or more transition metals contained in the catalyst may be dispersed at the single-atom size within the carbon composite.

[0073] In this specification, the term "single atom catalyst (SAC)" refers to a catalyst in which the catalytically active site is represented at the atomic level, and the carbon composite may include a single atom catalyst containing a transition metal as the catalyst.

[0074] According to one aspect of the present invention, the catalyst does not need to contain metallic bonds between transition metals in its structure. That is, the catalyst does not need to contain metal particles formed via metallic bonds between two or more transition metal atoms in its structure. Specifically, the carbon composite according to one aspect of the present invention does not contain metallic bonds between two or more transition metals contained in the catalyst.

[0075] In one embodiment of the present invention, the inclusion of the transition metal in a form dispersed at the single-atom size on a porous carbon material and / or organic support can be confirmed, for example, by microscopic observation of the carbon composite and / or catalyst using a scanning electron microscope (SEM), a transmission electron microscope (TEM), or a scanning transmission electron microscope (STEM).

[0076] In another aspect of the present invention, the catalyst contained in the carbon composite may include particles containing one or more transition metals, in which case the average diameter (D 50 The average diameter of the particles (D) can be, for example, 1 to 30 nm, which is the diameter of a single atom constituting the transition metal. Specifically, the average diameter of the particles (D) 50 The particles may have a diameter 1 to 5 times the diameter of a single atom constituting the transition metal. Preferably, the average diameter of the particles (D 50 The diameter of the transition metal can be 1 to 3 times the diameter of a single atom constituting the transition metal, more preferably 1 time the diameter of a single atom constituting the transition metal. That is, it is most preferable that the catalyst has a form in which the transition metal is dispersed in the carbon composite at the size of a single atom.

[0077] In one embodiment of the present invention, the absence of metallic bonds between two or more transition metals in the catalyst can be confirmed, for example, by X-ray diffraction (XRD) analysis of the carbon composite and / or the catalyst.

[0078] In one embodiment of the present invention, the transition metal contained in the catalyst is not particularly limited as long as it can exhibit activity in the oxidation / reduction reaction of sulfur at the positive electrode of a lithium-sulfur battery, but may be, for example, zinc (Zn), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), rubidium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), cadmium (Cd), lanthanum (La), hafnium (Hf), tantalum (Ta), tungsten (W), osmium (Os), iridium (Ir), cerium (Ce), galadium (Gd), scandium (Sc), titanium (Ti), gallium (Ga), indium (In), or two or more of these.

[0079] In another embodiment of the present invention, the transition metal contained in the catalyst may be iron (Fe).

[0080] In one embodiment of the present invention, the diameter of a known iron (Fe) atom is 300 pm, and when the catalyst contained in the carbon composite of the present invention contains iron (Fe), the transition metal present in the carbon composite is, for example, a diameter of 0.3 nm to 5 nm (D 50 It can be confirmed that it has the diameter (D) of the iron contained in the carbon composite. For example, the diameter (D) of the iron contained in the carbon composite. 50 ) may be 0.5nm to 2nm, 0.3nm to 1.5nm, 0.3nm to 1nm, or 0.3nm to 0.5nm.

[0081] In one embodiment of the present invention, the nonmetallic element that forms a ligand with the transition metal in the catalyst can be appropriately selected depending on the type of transition metal, and is not particularly limited.

[0082] In another embodiment of the present invention, the nonmetallic elements that form ligands with the transition metal in the catalyst may be, for example, hydrogen (H), boron (B), nitrogen (N), oxygen (O), fluorine (F), neon (Ne), silicon (Si), phosphorus (P), chlorine (Cl), bromine (Br), iodine (I), or two or more of these.

[0083] In yet another embodiment of the present invention, if the catalyst contains iron (Fe) as a transition metal, it may also contain nitrogen (N) as a nonmetallic element. The catalyst may be advantageous in that it exhibits excellent catalytic activity when the iron forms a ligand with nitrogen, but the present invention is not limited thereto.

[0084] In one embodiment of the present invention, if the catalyst contains iron (Fe) as a transition metal and nitrogen (N) as a nonmetallic element, the catalyst may include a structure in which one iron (Fe) atom is bonded to four adjacent nitrogen (N) atoms. While including a structure in which one iron atom is bonded to four adjacent nitrogen atoms can provide advantageous effects in terms of the activity stability of the carbon composite, the present invention is not limited thereto.

[0085] As described above, since the catalyst is located on the outer surface and / or the inner surface of the pores of the carbon material doped with at least one sulfur, the carbon composite according to the present invention can improve catalytic activity in sulfur oxidation / reduction reactions.

[0086] In one embodiment of the present invention, the porous carbon material doped with at least one sulfur may be a porous carbon material produced by carbonizing precursors of various carbon materials and then doped with at least one sulfur.

[0087] The porous carbon materials produced by carbonizing the various carbon material precursors mentioned above are not particularly limited as long as they are commonly used in the art. For example, the porous carbon materials include graphite; graphene; reduced graphene oxide (rGO); carbon blacks such as Denka Black, acetylene Black, Ketjen Black, Channel Black, Furnace Black, Lamp Black, and Thermal Black; carbon nanotubes (CNTs) such as single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs); carbon fibers such as graphite nanofibers (GNFs), carbon nanofibers (CNFs), and activated carbon fibers (ACFs); graphite and activated carbon such as natural graphite, artificial graphite, and expanded graphite; fullerenes; or activated carbon obtained by activating carbon materials.

[0088] According to the present invention, the carbon composite has a structure in which at least one sulfur is doped into a porous carbon material as described above.

[0089] In the present invention, the porous carbon material doped with at least one sulfur has a structure in which at least one carbon atom (C) of the porous carbon material is substituted with sulfur.

[0090] In one aspect of the present invention, the sulfur content doped into the porous carbon material may be, for example, such that the molar ratio of sulfur doped into the porous carbon material to one or more transition metals contained in the catalyst is 0.5 to 8. Specifically, the molar ratio of sulfur doped into the porous carbon material to one or more transition metals contained in the catalyst may be 0.5 to 5 or 1 to 3. When the molar ratio of the transition metal to sulfur is within the above range, advantageous effects in terms of catalytic activity can be obtained, but the present invention is not limited thereto.

[0091] The molar ratio of sulfur doped into the porous carbon material to the transition metal in the catalyst can be measured, for example, by inductively coupled plasma mass spectrometry (ICP-MS). While it may be advantageous to use a high-resolution instrument for measurement accuracy when the amount of doped sulfur is trace, the present invention is not limited thereto.

[0092] In one embodiment of the present invention, the at least one sulfur can be doped in the form of a sulfur atom or a sulfur compound.

[0093] Specifically, the doping of sulfur in the form of sulfur atoms indicates that the structure of the porous carbon material contains a -CSC- structure in which carbon atoms are substituted with sulfur atoms. Furthermore, the doping of sulfur in the form of sulfur compounds indicates that the structure of the porous carbon material contains a -C-SY-C- structure (where SY represents a sulfur compound) in which carbon atoms are substituted with sulfur compounds.

[0094] In one embodiment of the present invention, the form of the sulfur compound is, for example, a sulfur oxide (SO4). x It can exhibit the form (0.1 ≤ x ≤ 4).

[0095] In one embodiment of the present invention, the at least one sulfur-doped porous carbon material may include a structure in which the sulfur is doped in the form of sulfur dioxide (SO2). Specifically, the sulfur-doped porous carbon material may include a -C-SO2-C- structure within its structure.

[0096] In one embodiment of the present invention, the porous carbon material doped with at least one sulfur may include a first structure according to the following formula 1 and / or a second structure according to the following formula 2 within its structure.

[0097] [Formula 1] -C-SO2-C- [Formula 2] -CSC-

[0098] In one aspect of the present invention, the at least one sulfur within the carbon composite can adjust the orbital levels of the transition metal present in the catalyst, for example, allowing electrons to move between the sulfur-doped position (i.e., the EEB site) and the transition metal.

[0099] In this case, the orbital level sequence of the transition metal and the EEB site is determined according to the type of transition metal, and the transition metal may function as an electron donor and the EEB site may function as an electron acceptor, or the transition metal may function as an electron acceptor and the EEB site may function as an electron donor.

[0100] In one embodiment of the present invention, the carbon composite may contain iron (Fe) as a transition metal in the catalyst, and the first and second structures may be contained within the structure of the porous carbon material doped with at least one sulfur. In this case, the roles of the transition metal and electron donors and / or electron acceptors at the EEB site can be determined according to the ratio (first structure / second structure) of the first and second structures that are in positions to coordinate with the transition metal in one of the catalysts.

[0101] In one embodiment of the present invention, the electron donor / acceptor relationship between the transition metal and the EEB site can be confirmed by measuring their orbital levels, but the mechanism of the present invention is not limited thereto.

[0102] For example, if the orbital level of the catalytically active transition metal in the carbon composite is low, electrons will move from the transition metal to the EEB site, or if the orbital level of the transition metal is high, electrons will move from the EEB site to the transition metal.

[0103] In one embodiment of the present invention, if the ratio of the first structure to the second structure is high, the d-orbital (orbital) level of iron (Fe) is lowered due to the stabilization of the iron (Fe) d-orbital (orbital) of -SO2, which may result in the activity of electrons moving from iron to the EEB site.

[0104] In another embodiment of the present invention, if the ratio of the first structure to the second structure is low, the stabilizing effect decreases, and the d-orbital (orbital) level of iron increases, which may result in an activity that causes electrons to move from the EEB site to iron.

[0105] In this specification, the ratio of the first structure to the second structure may be expressed, for example, as a molar ratio.

[0106] As a result, in one embodiment of the present invention, when the transition metal in the catalyst of the carbon composite contains iron (Fe), the catalytic activity can be further improved by electrons moving from the EEB site to the iron (Fe), so the ratio of the first structure to the second structure (first structure / second structure ratio) in the structure of the at least one sulfur-doped porous carbon material can preferably be 1 or less. The ratio of the first structure to the second structure (first structure / second structure ratio) can be, for example, 1 or less, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, or 0.15 or less. Alternatively, the first structure / second structure ratio can be 0.01 or more, 0.05 or more, or 0.1 or more. For example, the ratio of the first structure to the second structure may be 0.01 or more and 1 or less, 0.05 or more and 0.8 or less, 0.10 or more and 0.7 or less, 0.10 or more and 0.5 or less, or 0.10 or more and 0.2 or less, but the present invention is not limited to these.

[0107] According to one aspect of the present invention, the carbon composite, when used as a positive electrode, contains numerous micropores for supporting the positive electrode active material and / or the catalyst within the carbon composite.

[0108] In one embodiment of the present invention, the carbon composite contains numerous micropores on its outer surface and internally, and these micropores can be classified according to their size into nanopores with a diameter of less than 10 nm and macropores with a diameter of 10 nm or more.

[0109] In one embodiment of the present invention, the diameter of the nanopores is less than 10 nm, and specifically may be 1-9.5 nm, 2-9 nm, 3-8 nm, 3.5-7 nm, 4-6 nm, 4-5 nm, or 4.0-4.5 nm.

[0110] In another embodiment of the present invention, the diameter of the macropores is 10 nm or more, and specifically may be 10 nm to 50 nm, 40 nm or less, 30 nm or less, or 20 nm or less. More specifically, the diameter of the macropores may be 10 nm to 19 nm, 10 nm to 18 nm, 12 to 18 nm, 13 to 17 nm, or 14 to 15 nm.

[0111] The diameter of the micropores can be measured by methods known in the industry for measuring the diameter of pores in porous materials, and the measurement method is not particularly limited. For example, the diameter of the micropores can be measured using a scanning electron microscope (SEM), a field-emission electron microscope (FE-SEM), or a laser diffraction method.

[0112] In one embodiment of the present invention, the carbon composite may be mixed with an active material to exert a more favorable effect in mediating the activation of the lithium polysulfide conversion reaction when the total number of macropores is greater than the total number of nanopores.

[0113] In another embodiment of the present invention, when N(nano) is the number of pores with a diameter of less than 10 nm among all pores of the carbon composite, and N(macro) is the number of pores with a diameter of 10 nm or more, the ratio of N(macro) to N(nano) is the ratio of N(macro) / N(nano), which may be 1 or more.

[0114] In one embodiment of the present invention, the average particle size (D) of the carbon composite. 50 ) could be, for example, 0.5 μm to 200 μm, 0.5 μm to 200 μm, 1 μm to 150 μm, or 10 μm to 150 μm.

[0115] In one embodiment of the present invention, for the usefulness of the lithium-sulfur battery, the BET specific surface area of ​​the carbon composite is, for example, 200 m². 2 It may be greater than or equal to / g, but is not limited to this.

[0116] Specifically, the BET specific surface area of ​​the carbon composite is not particularly limited to an upper limit, but for example, 200 m² 2 / g or more, 300m 2 / g or more, 400m 2 / g or more, 500m 2 / g or more, 600m 2 / g or more, 700m 2 / g or more 1,500m 2 / g or less, 1,000m 2 / g or less, 900m 2 / g or less, 800m 2 / g or less, 780m 2 / g or less, 750m 2 It may be less than / g. The carbon composite according to the present invention contains a large number of micropores, and the catalyst supported thereon may have a form in which a single-atom-sized transition metal is dispersed in a porous carbon material and / or organic support, thus having the advantage of a very large specific surface area.

[0117] The BET specific surface area may be a value measured by the BET method and according to a known method for measuring BET specific surface area. For example, the BET specific surface area may be a value calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using BELSORP-mino II manufactured by BEL Japan.

[0118] In one embodiment of the present invention, the pore volume of the carbon composite is, for example, 1 to 10 cm². 3 It can be / g. Specifically, the pore volume of the carbon composite is 1 to 10 cm³. 3 / g, 2-8cm 3 / g, 3-6cm 3 / g, 4-5cm 3 / g, 1-3cm 3 / g, or 1-2cm 3 It could be / g, but is not limited to these.

[0119] The pore volume may be a value calculated and measured, for example, by N2 isotherm analysis based on the adsorption of liquid nitrogen.

[0120] In one embodiment of the present invention, the carbon composite has a Raman peak intensity ratio (I G / I D The ratio may be 1 or less. For example, the above I G / I D The ratio may be 0.1 to 1, 0.5 to 1, or 0.8 to 1.0. G / I D When the ratio is within the above range, it can exhibit advantageous effects in terms of catalyst loading efficiency and / or sulfur doping efficiency on porous carbon materials, but the present invention is not limited thereto.

[0121] The aforementioned Raman peak intensity ratio is obtained from the spectrum of the carbon composite obtained by Raman spectroscopy. G and I D It can be measured by its value. In the resulting spectrum, I G This refers to the peak of the crystalline portion (G-peak, 1573 / cm), and I D This represents the peak in the amorphous region (D-peak, 1309 / cm). Therefore, in this case, I G / I D A smaller specific value indicates lower crystallinity.

[0122] In one aspect of the present invention, the carbon composite may have a transition metal content of, for example, 1% to 20% by weight, specifically 1% to 10% by weight, relative to the total weight of the carbon composite. When the transition metal content is within the above range, it may be advantageous in that the carbon composite exhibits an excellent catalytic effect while also exhibiting the effect of well dispersing the transition metal at the single-atom size and increasing the specific surface area of ​​the carbon composite. For example, when the transition metal content in the carbon composite exceeds the above range, the carbon composite may form metallic bonds between the transition metals and contain the transition metal in the form of metallic particles.

[0123] In one embodiment of the present invention, the carbon composite may have a sulfur (S) content of, for example, 0.1% to 10% by weight, specifically 1% to 5% by weight, relative to the total weight of the carbon composite. When the sulfur content is within the above range, it may be advantageous in terms of exhibiting an effect that enhances the catalytic efficiency of the transition metal.

[0124] In another embodiment of the present invention, as described above, the carbon composite may contain iron as a transition metal, and the catalyst may have a form in which iron is dispersed on an organic support at a single-atom size, and the iron forms ligands with four surrounding nitrogen atoms. That is, when such a structure is represented as Fe-N4, sulfur doped into a porous carbon material is present around the Fe-N4, and the sulfur that can form a coordination bond with the iron of Fe-N4 may exist in the form of -C-SO2-C- (first structure) and / or -CSC- (second structure). In this case, the ratio of the first structure to the second structure may be 1 or less, as described above, and specifically may be 0.1 to 0.7. The sulfur content in the carbon composite may be determined within the range that satisfies the above ratio. In this case, the ratio of the first structure to the second structure may be expressed as a molar ratio as described above.

[0125] The ratio of the first structure to the second structure may be, for example, 1 or less, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, 0.2 or less, or 0.15 or less. Alternatively, the ratio of the first structure to the second structure may be, for example, 0.01 or more, 0.05 or more, or 0.1 or more. For example, the ratio of the first structure to the second structure may be 0.01 to 1 or less, 0.05 or more, 0.8 or less, 0.10 to 0.7 or less, 0.10 to 0.5 or less, or 0.10 to 0.2 or less, but the present invention is not limited thereto.

[0126] As described above, the carbon composite of the present invention has sulfur present that can exchange electrons with the transition metal around the catalyst containing the transition metal, and at the same time provide an additional binding site with lithium polysulfide. Therefore, when used in the positive electrode of a lithium-sulfur battery, it can play a role in improving battery efficiency, but the mechanism of the present invention is not limited to this.

[0127] According to one aspect of the present invention, the carbon composite is a support that carries a sulfur-based compound which is a positive electrode active material, and can be further compounded with the sulfur-based compound and used as a positive electrode active material, or the carbon composite itself can be used as a substitute for a conductive material.

[0128] In particular, the carbon composite of the present invention can exhibit the effect of significantly improving the utilization rate of atoms in the carbon composite by dispersing the transition metal at the single-atom size, but the mechanism of the present invention is not limited to this.

[0129] Another aspect of the present invention provides a method for producing the carbon composite described above.

[0130] A method for producing a carbon composite according to another aspect of the present invention includes (S1) doping a porous carbon material with at least one sulfur, and (S2) impregnating the result of step (S1) with a transition metal-containing precursor solution, and then removing the solvent. Specifically, step (S1) includes heat treatment while the sulfur-doped precursor and the porous carbon material are in contact.

[0131] Step (S1) is a step to dope a porous carbon material with sulfur to form electron-exchangeable bonding (EEB) sites for the catalyst.

[0132] In one embodiment of the present invention, step (S1) may include, for example, impregnating the porous carbon material with a sulfur-containing solution containing a sulfur-doping precursor, and then heat-treating it.

[0133] In one embodiment of the present invention, step (S1) may be carried out, for example, by impregnating the porous carbon material with a sulfur-containing solution, grinding it until the solvent evaporates, and then heat-treating it, but the present invention is not limited thereto.

[0134] In one embodiment of the present invention, moistening the porous carbon material with a sulfur-containing solution can be performed, for example, by impregnating the porous carbon material with the sulfur-containing solution or by immersing the porous carbon material in the sulfur-containing solution, but the present invention is not limited thereto.

[0135] In one embodiment of the present invention, the heat treatment may be carried out at, for example, 800°C to 1,000°C to form a low ratio of -C-SO2-C-(first structure) / -CSC-(second structure) at the EEB site.

[0136] In one embodiment of the present invention, the heat treatment may include raising the temperature while maintaining a constant rate selected from the range of 2°C / min to 10°C / min.

[0137] In one embodiment of the present invention, the heat treatment may be carried out while increasing the temperature at a rate of 5°C / min.

[0138] In one embodiment of the present invention, after contacting the porous carbon material with a sulfur-containing solution as described above, sulfur is uniformly doped into the porous carbon by pulverization and heat treatment, thereby forming a uniform EEB within the porous carbon. As a result, the catalyst described later may have a form in which the transition metal is uniformly dispersed at the single-atom size, but the manufacturing method of the present invention is not limited to this.

[0139] The sulfur-containing solution may be a solution obtained by dissolving a sulfur-doped precursor in a solvent, and the sulfur-doped precursor may be, for example, dibenzyl disulfide (DBDS), sodium metabisulfite (Na2S2O5), sodium pyrosulfate (Na2S2O7), sodium thiosulfate (Na2S2O3), thiourea (CH4N2S), sodium sulfide (Na2S), potassium thiocyanate (KSCN), benzyl mercaptan (C7H8S), benzothiophene (C8H6S), or dibenzothiophene (C7H6S). 12 The solvent may be H8S, dibenzohiophene, or a mixture thereof. The solvent is not particularly limited and can be selected as appropriate, as long as it is a solvent for the sulfur-doped precursor and has excellent wettability with the porous carbon material.

[0140] According to one aspect of the present invention, the form and structure of sulfur doping in the porous carbon material may differ depending on the type of sulfur-doped precursor. In this case, since sulfur plays the role of an EEB site, and can supply abundant electrons to the transition metal, the sulfur doping may be carried out using dibenzyl disulfide dissolved in an alcohol-based solvent such as ethanol.

[0141] According to one aspect of the present invention, the sulfur doping may be carried out using dibenzyl disulfide, and the ratio of -C-SO2-C-(first structure) / -CSC-(second structure) in the carbon composite produced at this time may be 0.1 to 0.5.

[0142] According to another aspect of the present invention, the sulfur doping may be carried out using sodium sulfite, and the ratio of -C-SO2-C-(first structure) / -CSC-(second structure) in the carbon composite produced at this time may be 0.5 to 1.

[0143] Step (S2) may include the step of preparing a precursor solution for producing a catalyst supported on a sulfur-doped porous carbon material.

[0144] In one aspect of the present invention, the transition metal-containing precursor solution is a precursor solution for producing a catalyst, and may include an organic solvent and a transition metal precursor compound.

[0145] In one aspect of the present invention, the transition metal-containing precursor solution is a precursor solution for producing a catalyst and may comprise an organic solvent, a precursor compound of a nonmetallic element, and a precursor compound of a transition metal.

[0146] In one embodiment of the present invention, the transition metal precursor compound may be, for example, an oxide, halide, acetate, nitrate, sulfide, cyanide, fatty acid salt or phosphonate of a saturated or unsaturated carbon chain of a transition metal, or a mixture of two or more of these.

[0147] In one embodiment of the present invention, the transition metal halide may be, for example, a transition metal fluoride, a transition metal chloride, a transition metal bromide, or a transition metal iodide.

[0148] In another embodiment of the present invention, the precursor solution may contain iron trichloride (FeCl3), ferrocene, iron acetylacetonate, iron nitrate, ferrous sulfate, potassium iron ferricyanide, or a mixture of two or more of these.

[0149] In one aspect of the present invention, the precursor compound of the nonmetallic element may be an organic compound containing at least one nonmetallic element.

[0150] In one embodiment of the present invention, the organic compound containing at least one nonmetallic element is a compound containing the nonmetallic element described above. The nonmetallic element may be, for example, nitrogen (N), and the organic compound containing nitrogen may be, for example, 1,10-phenanthroline, polyaniline, polydopamine, melamin, carbon nitride (g-CN, carbon nitride), phenylenediamine, or a mixture of two or more of these.

[0151] In one embodiment of the present invention, the organic solvent is a solvent for organic compounds containing at least one nonmetallic element and halides of transition metals, and can be appropriately selected and used, and is not particularly limited.

[0152] In one embodiment of the present invention, the molar ratio of the nonmetal element precursor compound to the transition metal halide in the precursor solution may be, for example, 50:1 to 1:1, 40:1 to 1:1, 20:1 to 1:1, 10:1 to 1:1, or 5:1 to 1:1, but is not limited thereto.

[0153] In one embodiment of the present invention, the molar ratio of the nonmetal element precursor compound to the transition metal halide in the precursor solution may be, for example, 4:1.

[0154] In one embodiment of the present invention, the step of producing a transition metal-containing precursor solution may be further included before step (S2). In this case, the step of producing the transition metal-containing precursor solution can be carried out in any order in relation to step (S1). For example, the step of producing the transition metal-containing precursor solution can be carried out after step (S1), or step (S1) can be carried out after the step of producing the transition metal-containing precursor solution, or the step of producing the transition metal-containing precursor solution can be carried out simultaneously with step (S1). Thus, the order in which step (S1) and the step of producing the transition metal-containing precursor solution are carried out is not particularly limited.

[0155] Step (S2) is the step of positioning at least one catalyst containing a transition metal on at least one of the outer surface and the inner surface of the pores of the porous carbon material doped with at least one sulfur produced in (S1).

[0156] For this purpose, step (S2) includes impregnating the transition metal-containing precursor solution with the result of step (S1), and then removing the solvent.

[0157] In one embodiment of the present invention, step (S2) may include impregnating the result of step (S1) into the transition metal-containing precursor solution, followed by grinding and drying. The drying may be carried out at, for example, 70°C to 100°C, but is not limited thereto. According to another embodiment of the present invention, the drying may further include a step of heat treatment at, for example, 800°C to 1,000°C.

[0158] In one embodiment of the present invention, the step (S3) may further include, after step (S2), a step of cooling the result obtained from step (S2) to room temperature and then treating it with acid.

[0159] According to the method described above, a carbon composite can be produced comprising a porous carbon material doped with at least one sulfur and at least one catalyst containing one or more transition metals, wherein the catalyst is located on at least one of the outer surface and the inner surface of the pores of the porous carbon material doped with at least one sulfur.

[0160] According to yet another aspect of the present invention, a positive electrode is provided which comprises a positive electrode active material including the carbon composite and sulfur-based compound described above.

[0161] The positive electrode may use the above-mentioned carbon composite as a support for the positive electrode active material, and may include a composite formed by mixing this with a sulfur-based compound, which is the positive electrode active material, as the positive electrode active material.

[0162] In one embodiment of the present invention, the sulfur-based compound is, for example, sulfur (S8), lithium sulfide (Li2S), lithium polysulfide (Li2S x This may be, but is not limited to, a disulfide compound (2 ≤ x ≤ 8), or a mixture of two or more of these.

[0163] In one embodiment of the present invention, the carbon complex and the sulfur compound are determined according to the sulfur content in the carbon complex and the type of sulfur compound, and are not particularly limited, but for example, the carbon complex and the sulfur compound can be mixed in a content ratio of 1:9 to 9:1. Specifically, they can be mixed in a content ratio of 1:9 to 5:5, and more specifically, 2:8 to 4:6.

[0164] In one embodiment of the present invention, the positive electrode active material may be formed by mixing the carbon composite and a sulfur-based compound and then heat-treating the mixture. The heat treatment may be carried out at a temperature of, for example, 130°C to 180°C, specifically 150°C to 160°C.

[0165] In one embodiment of the present invention, the positive electrode for a lithium-sulfur battery may further include a binder in addition to the positive electrode active material comprising a carbon composite and a sulfur-based compound. The binder is not particularly limited as long as it is a binder used in the positive electrode of a lithium-sulfur battery.

[0166] In another embodiment of the present invention, the positive electrode for the lithium-sulfur battery may further include a conductive material, additives, etc., in addition to the positive electrode active material and binder. In this case, ordinary binders, conductive materials, and additives can be used, so a description of specific types will be omitted.

[0167] In yet another embodiment of the present invention, the positive electrode for the lithium sulfur battery may include a positive electrode current collector and a positive electrode active material layer in which the positive electrode active material is coated on one or both sides of the current collector together with a binder.

[0168] In this case, the positive electrode current collector is not particularly limited as long as it has high conductivity without inducing a chemical change in the battery.

[0169] In one embodiment of the present invention, the cathode containing the carbon composite can exhibit excellent effects in terms of initial capacity and cycle stability, but the effects of the present invention are not limited thereto.

[0170] In one embodiment of the present invention, the positive electrode for the lithium-sulfur battery is, for example, 1.0 mg / cm³. 2 The sulfur (S) loading amount may be greater than or equal to the above. For example, the sulfur loading amount in the positive electrode of the lithium sulfur battery may be 1 mg / cm³. 2 More than 1.5mg / cm 2 More than 2mg / cm 2 For example, 2 mg / cm³ 2 ~10 mg / cm³ 2 And yet, it can exhibit the effect of demonstrating driving stability.

[0171] A lithium-sulfur battery according to yet another aspect of the present invention comprises a positive electrode, a negative electrode, a separation membrane interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode comprises the above-mentioned carbon composite and sulfur-based compound as positive electrode active material.

[0172] In one embodiment of the present invention, the negative electrode, separation membrane, and electrolyte can be used without particular limitations as long as they are suitable for use in a lithium-sulfur battery without impairing the purpose of the present invention; therefore, a description of specific types thereof will be omitted.

[0173] In one embodiment of the present invention, the external shape of the lithium-sulfur battery may be, for example, coin-shaped, cylindrical, pouch-shaped, or rectangular, but is not particularly limited. Furthermore, the lithium-sulfur battery can be used not only as a battery cell used as a power source for small devices, but also as a unit battery in medium- to large-sized battery modules containing multiple battery cells, and there are no particular restrictions on its usage.

[0174] In one embodiment of the present invention, a lithium-sulfur battery using a positive electrode containing the carbon composite is not only superior in terms of initial capacity and cycle stability, but also exhibits excellent effects in terms of the energy density of the battery. However, the effects of the present invention are not limited to this.

[0175] In one embodiment of the present invention, the lithium-sulfur battery can significantly improve energy density by increasing the amount of sulfur loaded into the electrodes and reducing the amount of electrolyte, but the effects of the present invention are not limited to this.

[0176] In one embodiment of the present invention, the lithium-sulfur battery may have an electrolyte / sulfur (E / S) ratio of 10 μL / mg or less. For example, the E / S ratio of the lithium-sulfur battery may be 10 μL / mg or less, 8 μL / mg or less, 6 μL / mg or less, 4 μL / mg or less, or 2 μL / mg or less. Conventionally, there was a limit to how much the E / S ratio could be reduced due to the low activity of the positive electrode, but since the present invention has the effect of stably reducing the E / S ratio, the E / S ratio of the lithium-sulfur battery may exceed the above range, and it is obvious to those skilled in the art that there is no lower limit, and the present invention is not limited thereto.

[0177] In another embodiment of the present invention, the lithium-sulfur battery may have an electrolyte / capacity (E / C) ratio of 10 μL / mAh or less. For example, the E / C ratio of the lithium-sulfur battery may be 10 μL / mAh or less, 9 μL / mAh or less, 8 μL / mAh or less, 7 μL / mAh or less, 5 μL / mAh, or 4 μL / mAh or less, but the present invention is not limited thereto. The electrolyte / capacity (E / C) ratio of the lithium-sulfur battery may be, for example, 1 μL / mAh or more, but the present invention is not limited thereto.

[0178] According to yet another aspect of the present invention, a cathode is provided which contains the above-mentioned carbon composite as a cathode additive and a sulfur-based compound as a cathode active material.

[0179] In one aspect of the present invention, the carbon composite is used as a support and is included in the positive electrode in the form of a positive electrode active material formed by compounding the carbon composite with a sulfur-based compound. Apart from this aspect of the present invention, the carbon composite may be included in the positive electrode as an additive that replaces a conductive material.

[0180] In one embodiment of the present invention, using the carbon composite as a cathode additive may not only improve the battery capacity but also improve battery performance by enhancing its reactivity with lithium polysulfide.

[0181] In one embodiment of the present invention, when the carbon composite is used as a positive electrode additive, the carbon composite may be included in an amount of 1 to 25% by weight, for example, 1 to 15% by weight, or 1 to 10% by weight, relative to the total weight of the positive electrode active material, binder, and carbon composite contained in the positive electrode active material layer, but is not limited thereto.

[0182] In one embodiment of the present invention, the positive electrode can be a sulfur-based compound as the positive electrode active material, or a conventional carbon support on which the sulfur-based compound is supported. The configuration of the positive electrode described above is applied to the sulfur-based compound. The conventional carbon support may be, for example, carbon nanotubes, but is not limited thereto.

[0183] According to yet another aspect of the present invention, a lithium-sulfur battery is provided, comprising a positive electrode, a negative electrode, a separation membrane interposed between the positive and negative electrodes, and an electrolyte, as described above, using a carbon composite as a positive electrode additive.

[0184] In yet another aspect of the present invention, a battery is provided in which the carbon composite described above is included in at least one of the electrodes, a positive electrode and a negative electrode. In this battery, the battery may include a positive electrode, a negative electrode, a separator membrane interposed between the positive and negative electrodes, and an electrolyte, and is not particularly limited to a lithium-sulfur battery.

[0185] In this case, the components other than the negative electrode, separation membrane, electrolyte, and carbon composite of the positive electrode will be based on the battery configuration described above.

[0186] Figure 2a shows a schematic flowchart of a process according to one aspect of the present invention, in which a carbon composite is produced by doping porous carbon with at least one sulfur, forming a transition metal-containing catalyst, and then mixing this with a sulfur-based compound to produce a cathode active material.

[0187] The following describes in detail, with reference to examples, a method for producing a carbon composite according to one aspect of the present invention and a method for producing a positive electrode active material using the same. However, the following examples are merely illustrative of the present invention, and the scope of the present invention is not limited by these examples.

[0188] Manufacturing Example 1. Synthesis of porous carbon material (MSU-FC) The porous carbon material was synthesized using the hard template method through the following process.

[0189] First, poly(ethylene glycol)-block-polypropylene glycol)-block-poly(ethylene glycol) (P123, Mn: ~5800 g / mol, manufactured by Sigma-Aldrich) was dissolved in distilled water (DI water) (160 ml) and glacial acetic acid (99.8%, SAMCHUN Pure Chemical Co., Ltd.) (4.58 ml). Next, mesitylene (Merck Millipore) (9.26 ml) was added dropwise, and the mixture was stirred for 1 hour to prepare the P123 solution.

[0190] A sodium silicate solution was prepared by dissolving 15.5 ml of sodium silicate (Sigma Aldrich) in 240 ml of distilled water. The prepared sodium silicate solution was added to the P123 solution prepared above, stirred for 5 minutes, and then stored at 40°C for 20 hours without stirring. After that, it was aged in an oven at 100°C for 24 hours. The aged solution was filtered and redissolved in a mixture of 200 ml of distilled water and 5 ml of HCl solution (35.0-37.0%, SAMCHUN Pure Chemical Co., Ltd.). After 3 hours, the solution was filtered again and calcined at 550°C for 4 hours to obtain mesoporous silica (MSU-F-SiO2).

[0191] The obtained mesoporous silica was uniformly dispersed in ethanol, and AlCl3·6H2O (98%, Kanto Chemical Co., Ltd.) (0.21g) was mixed to obtain a homogeneous mixture. Next, the obtained mixture was dried in an oven at 60°C to remove the ethanol, and the mixture was calcined at 550°C for 4 hours to obtain mesoporous silica (Al-MSU-F-SiO2) with introduced Al acid sites.

[0192] The Al-MSU-F-SiO2 mold, used as a hard mold, was impregnated with furfuryl alcohol (manufactured by Sigma-Aldrich) as a carbon precursor, and then heat-treated at 850°C for 4 hours under an Ar atmosphere. After cooling to room temperature, the Al-MSU-F-SiO2 mold was etched with HF solution (manufactured by JT Baker) to produce the porous carbon material (MSU-FC) of Production Example 1.

[0193] Example 1. Production of carbon composite (FeNC-EEB-1) Step 1. Sulfur doping within porous carbon material (formation of EEB sites) A DBDS solution was prepared by dissolving dibenzyl disulfide (DBDS, 98%) in ethanol (100 ml).

[0194] The porous carbon material (MSU-FC) manufactured as described above was uniformly impregnated with the DBDS solution, and then repeatedly ground until the ethanol completely evaporated. Next, the DBDS-impregnated porous carbon (DBDS-impregnated MSU-FC) was dried at 80°C for 1 hour, and then heat-treated at 900°C for 1 hour under an Ar atmosphere to form EEB sites with a low molar ratio of -SO2 / -S.

[0195] Step 2. Introduction of transition metal catalyst To support the transition metal catalyst on the outer surface and inner surface of the pores of porous carbon on which the EEB sites were formed, a transition metal-containing precursor solution was prepared by dissolving FeCl3·6H2O (Sigma-Aldrich) and 1,10-phenanthroline (99%, Sigma-Aldrich) in ethanol. Next, the precursor solution was immersed in the porous carbon material on which the EEB sites were formed, and then pulverized. The mixture was dried at 80°C for 1 hour, and then heat-treated at 900°C for 1 hour under an Ar atmosphere. After cooling to room temperature, the aggregated Fe metal residue was removed by stirring with 1M HCl to produce the carbon composite (FeNC-EEB-1) described in the title.

[0196] Example 2. Production of carbon composite (FeNC-EEB-2) The carbon composite (FeNC-EEB-2) was prepared in the same manner as in Example 1, except that Na2S2O5 (97%, Sigma-Aldrich) was used instead of DBDS for the formation of the EEB site.

[0197] Comparative Example 1. Production of carbon composite (FeNC) The carbon composite (FeNC) was prepared in the same manner as in Example 1, except that Step 1 was omitted to introduce the transition metal catalyst without forming an EEB site.

[0198] [Checking for sulfur doping] X-ray spectroscopy (XPS) (VG Scientific Escalab 250, Al Kα) was used to obtain 2p spectra of sulfur atoms (S) in the carbon composites of Example 1 and Example 2, and the results are shown in Figure 2b (Example 1) and Figure 2c (Example 2), respectively.

[0199] As shown in Figures 2b and 2c, both Example 1 and Example 2 exhibited two characteristic peaks for -S, 163.7 eV (CSC 2p 3 / 2) and 164.9 eV (CSC 2p 1 / 2), within the -CSC- structure formed by doping sulfur atoms within porous carbon, and a characteristic peak for -SO2, 168.0 eV (Oxidized S), within the -C-SO2-C- structure formed by doping with sulfur dioxide.

[0200] This confirmed that both Example 1 and Example 2 contain a structure in which sulfur is doped within porous carbon.

[0201] Next, the Fe content and molar ratio of the -SO2 / -S structure were measured for the carbon composites of Example 1, Example 2, and Comparative Example 1 using inductively coupled plasma atomic emission spectroscopy (ICP-AES), and the results are shown in Figure 2d.

[0202] As shown in Figure 2d, it was confirmed that the -SO2 / -S molar ratio at the EEB site differed between Example 1 and Example 2. Specifically, the -SO2 / -S molar ratio in Example 1 was 0.12, while the -SO2 / -S molar ratio in Example 2 was 0.63, which was approximately five times higher than that of Example 1. This was presumed to be because Na2S2O5, the precursor for sulfur doping in Example 2, had an even higher oxygen fraction compared to DBDS, and therefore formed the -SO2 species more stably at high temperatures.

[0203] Furthermore, Figure 3 shows mapping images obtained by energy dispersive spectroscopy (EDS) for Examples 1 and 2. The EDS mapping images were obtained from the distribution results of Fe single atoms and other components using a high-performance TEM (HR-TEM; Titan cubed G2 60-300). Figure 3 confirms that the Fe, N, C, S, and O atoms in Examples 1 and 2 are uniformly distributed along the particles. This confirms that EEB sites were formed within the carbon composite by doping with a transition metal-containing catalyst and sulfur. In particular, Figure 3 confirms that the nearest neighbor interatomic distance between Fe and S elements was formed to 2 nm or less within the carbon composites of Examples 1 and 2.

[0204] [Structural analysis of carbon complexes] The structures of the carbon composites of Example 1, Example 2, and Comparative Example 1, which were manufactured as described above, were confirmed by the following method.

[0205] Microscopic observation Figure 4 shows images obtained using SEM (S-4800 field emission, Hitachi, Ltd.) and TEM (G2 F30 S-Twin, Tencai) for each of the carbon composites of Example 1, Example 2, and Comparative Example 1. In Figure 4, FeNC represents the carbon composite of Comparative Example 1, FeNC-EEB-1 represents the carbon composite of Example 1, and FeNC-EEB-2 represents the carbon composite of Example 2. In each figure, the left image is the SEM image and the right image is the TEM image.

[0206] Analysis of stomatal properties For each of the carbon composites in Example 1, Example 2, and Comparative Example 1, the pore diameter (left) and relative pressure (right) were determined by nitrogen physicoadsorption analysis, and the results are shown in Figure 5.

[0207] Specifically, the specific surface area and pore size of the manufactured comparative examples and examples were analyzed using the following method.

[0208] First, to remove moisture and other substances physically adsorbed within the pores, the analyte was pre-treated by drying it overnight in a vacuum at 120°C. Next, liquid nitrogen at 77K was physically adsorbed onto the surface and pores of the analyte in a vacuum until the pressure was equilibrium. At this time, the specific surface area of ​​the porous material was calculated using the BET (Brunauer-Emmett-Teller) method based on the measured N2 isotherm. Furthermore, the pore volume value was obtained by the BJH (Barrett-Joyner-Halenda) method calculation based on the obtained N2 isotherm.

[0209] The measurement results for the surface area, pore diameter, and pore volume of the carbon composites of Example 1, Example 2, and Comparative Example 1 are shown in Table 1 below.

[0210] As can be seen in Figure 5, analysis of stomatal diameters revealed that the distribution of stomatal diameters exhibited a bimodal pattern. In Table 1 below, the peak appearing at the smaller diameter is designated as the first stomatal diameter peak, and the peak appearing at the larger diameter is designated as the second stomatal diameter peak.

[0211] [Table 1]

[0212] According to the results in Figures 4, 5 and Table 1, the carbon composites of Example 1, Example 2 and Comparative Example 1 each have a porous structure and a BET specific surface area of ​​700 m². 2 It was confirmed that the amount was greater than / g and that it contained pores of 4-5 nm and 10-15 nm, respectively.

[0213] Confirmation of the distribution of transition metals Figure 6 shows images obtained using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) for each of Comparative Example 1, Example 1, and Example 2. The HAADF-STEM images were obtained using a high-performance TEM (HR-TEM; Titan cubed G2 60-300) to show the distribution of single Fe atoms and other components. Figure 6 confirms that in Comparative Example 1, Example 1, and Example 2, the transition metal Fe is dispersed at the single-atom size within porous carbon.

[0214] Furthermore, the Fourier-transformed extended X-ray absorption fine structure (FT-EXAFS) results for Comparative Example 1, Example 1, and Example 2 are shown in Figure 7. To compare the chemical state of the iron elements distributed within the carbon composite with the chemical state of the iron metal, the evaluation results for the Fe foil are also shown in Figure 7.

[0215] As shown in Figure 7, Fe-Fe metallic bonds (2.2 Å) were confirmed in the Fe foil, whereas in Comparative Example 1, Example 1, and Example 2, Fe-Fe metallic bonds disappeared, and Fe-N (1.4 Å) and Fe-C (2.4 Å) peaks were newly formed. This confirmed that the catalyst (Fe-NC) present in Comparative Example 1, Example 1, and Example 2 does not contain Fe-Fe metallic bonds, i.e., Fe metal particles.

[0216] [Confirmation of catalytic function of carbon composites] Figure 8 shows graphs obtained using Fe K-edge XANES (X-ray absorption near-edge structure) analysis for the carbon composites of Example 1, Example 2, and Comparative Example 1.

[0217] As shown in Figure 8, the white line intensity of Example 1 was lower than that of Comparative Example 1, and the white line intensity of Example 2 was higher than that of Comparative Example 2. In other words, it was confirmed that Example 1 has a low -SO2 / -S ratio and exhibits an upshift of the Fe d-band center, thereby possessing the activity to transfer electrons from the EEB site to Fe.

[0218] On the other hand, Example 2 was found to have a high -SO2 / -S ratio and exhibit a downshift of the Fe d-band center, which confirmed that it may have the activity to transfer electrons from Fe to the EEB site.

[0219] This confirmed that the d-orbital (orbital) levels of the carbon composite can be adjusted by electron exchange depending on the ratio of -SO2 / -S in the sulfur-doped structure around the catalyst that can coordinate with the transition metal.

[0220] [Manufacturing of lithium-sulfur coin-type batteries] To confirm the sulfur and polysulfide conversion reaction activity of the carbon composite manufactured above, a lithium-sulfur coin-type battery was manufactured as follows.

[0221] Example 3 Manufacturing of positive electrodes A 30 wt% carbon composite (FeNC-EEB-1) prepared in Example 1 was mixed with 70 wt% sulfur (sulfur powder, manufactured by Sigma-Aldrich) and heated at 155°C for 8 hours to obtain a cathode active material.

[0222] To manufacture the working electrode, a cathode slurry was prepared by mixing the cathode active material manufactured above with PVDF (polyvinylidene fluoride) as a binder in a weight ratio of 9:1 using NMP (N-methyl-2-pyrrolidone) solvent.

[0223] The manufactured positive electrode slurry was coated onto carbon-coated aluminum foil and then dried at 60°C for 8 hours. After that, the electrode was pressurized and cut into coin shapes to produce the positive electrode.

[0224] Battery manufacturing A battery was manufactured by placing a positive electrode, a negative electrode, and a separator membrane between the positive and negative electrodes, along with an electrolyte, in a case.

[0225] The positive electrode manufactured as described above was prepared as the positive electrode, and a porous polypropylene membrane (Celgard 2400, Welcos Ltd) was prepared as the separation membrane. Lithium metal (200 μm thick) was prepared as the reference electrode and relative electrode, respectively. As the electrolyte, a solution was used consisting of a solvent (PANAX E-TEC Co., Korea) prepared by mixing dimethoxymethane and 1,3-dioxolane (DME / DOL) in a volume ratio of 1:1, containing 1.0 M LiTFSI (bis(trifluoromethane)sulfonamide lithium salt) as the electrolyte and 2.0 wt% LiNO3 (99.99% metal-based, manufactured by Sigma-Aldrich) as an additive.

[0226] The loading amount of sulfur in the positive electrode is 2.0 mg / cm³. 2 The E / S ratio of the battery was 10 μL / mg.

[0227] Example 4 The battery was manufactured in the same manner as in Example 3, except that Example 2 (FeNC-EEB-2) was used as the carbon composite during the manufacturing of the positive electrode.

[0228] Comparative Example 2 The battery was manufactured in the same manner as in Example 3, except that Comparative Example 1 (FeNC) was used as the carbon composite during the manufacturing of the positive electrode.

[0229] Manufacturing Example 2 The battery was manufactured in the same manner as in Example 3, except that the porous carbon material (MSU-FC) from Manufacturing Example 1 was used instead of the carbon composite during the manufacturing of the positive electrode.

[0230] [Performance evaluation of lithium-sulfur coin-type batteries] Using the lithium-sulfur coin-type battery manufactured as described above, the redox kinetic activity of lithium sulfide (Li2S) was evaluated using the following method.

[0231] First, Figure 9a shows the Tafel plots obtained to evaluate the redox kinetics of sulfur. According to Figure 9a, the Tafel plot for Example 3 in the positive electrode reaction was much lower than that of Comparative Example 2, while the Tafel plot for Example 4 was only slightly lower than that of Comparative Example 2. On the other hand, in the negative electrode reaction, both Example 3 and Example 4 showed lower Tafel slots than Comparative Example 2, which demonstrates that the doped sulfur around the catalyst, i.e., the -SO2 / -S EEB site, improved the redox kinetics of sulfur.

[0232] Next, to better understand the electrochemical dynamics of sulfur by the EEB site for the nucleation / decomposition behavior of lithium sulfide in the batteries of Examples 3 and 4, constant voltage analysis was performed, and the results are shown in Figures 9b and 9c. In Figures 9b and 9c, the capacity was calculated based on the weight of sulfur in the electrodes.

[0233] According to Figure 9b, the maximum current time t during constant voltage discharge at 2.05V is... m These were 227s (Example 3), 320s (Example 4), and 400s (Comparative Example 2), respectively. m The values ​​are the nucleation density (N0) and growth rate (k) of lithium sulfide, as shown in the formula below. 2 Considering that this is largely related to ), it was confirmed that the improvement in lithium sulfide nucleation in the battery of Example 3 led to a higher lithium sulfide nucleation capacity (213.3 mAh / g). Next, it was confirmed that Example 4 (196.8 mAh / g) had a slightly lower capacity than Example 3 (213.3 mAh / g), but exhibited even better capacity characteristics than Comparative Example 2 (185.3 mAh / g).

[0234] tm =(2πN0k 2 )-0.5

[0235] According to FIG. 9c, during the constant voltage charging at 2.35 V, Example 3 has a lower t m (468 s, Li2S dissociation capacity: 323.5 mAh / g) than Comparative Example 2 (t m (360 s) and a higher Li2S dissociation capacity (457.2 mAh / g) were confirmed. Also, Example 4 has a higher t m (489 s) and a higher Li2S dissociation capacity (381.5 mAh / g) than Comparative Example 2.

[0236] Thus, (i) by comparing the results of Comparative Example 2, Example 3, and Example 4, it was confirmed that introducing -SO2 / -S EEB sites formed by sulfur doping around the transition metal-containing catalyst can improve the kinetics of the conversion reaction involving lithium sulfide on the catalyst. In particular, (ii) it was confirmed that EEB sites with a low -SO2 / -S ratio (Example 3) are more effective in promoting the nucleation / decomposition reaction of lithium sulfide on the catalyst than EEB sites with a high -SO2 / -S ratio (Example 4).

[0237] Next, in order to evaluate the charge-discharge performance of the batteries of Comparative Example 2, Example 3, and Example 4, for the batteries of Comparative Example 2, Example 3, and Example 4, the charge-discharge performance was evaluated at a current density of 0.2 to 3.0 C rate (1 C rate to 1675 mA / g) and a voltage range of 1.7 to 2.8 V (vs. Li / Li + ), and the results are shown in FIG. 10.

[0238] FIG. 10(a) shows the initial voltage characteristics of the batteries of Comparative Example 2, Example 3, and Example 4 at a 0.2 C rate. According to this, it was confirmed that Comparative Example 2 also has a high initial discharge capacity (1125 mAh / g) due to the presence of the catalyst (FeNC), but the batteries of Example 3 (1324 mAh / g) and Example 4 (1179 mAh / g) have higher initial discharge capacities.

[0239] In addition to using FeNC-EEB-1 as a comparative group, the results of the battery (Production Example 2) in which the positive electrode was produced using the porous carbon (MSU-F-C) according to Production Example 1 are also shown in the results of FIG. 10(b). According to the results of FIG. 10(b), it was confirmed that the batteries of Example 3 (0.17 V) and Example 4 (0.185 V) were further improved compared to Comparative Example 2 (0.205 V) also in terms of the polarization degree.

[0240] FIG. 10(c) shows the measurement results of the discharge capacity ratio (rate capability) measured at different current densities of 0.3 to 2.0 C rates for the batteries of Comparative Example 2, Example 3, and Example 4. According to the results of FIG. 10(c), it was confirmed that in terms of the discharge capacity ratio, the measurements were in the order of Comparative Example 2 < Example 4 < Example 3, and the improvement degree of the discharge capacity ratio of Example 3 was the best.

[0241] FIG. 11 is a graph showing the measurement results of the discharge capacity measured while repeating charge and discharge 200 times at 0.2 C. According to FIG. 11, the battery of Comparative Example 2 showed a capacity of 864 mAh / g after 200 cycles, while the battery of Example 4 showed a capacity of 925 mAh / g, which was about 7% higher than that of Comparative Example 2, and the battery of Example 3 showed a capacity of 1030 mAh / g, which was about 10% higher than that of Example 4. As a result, it was confirmed that the batteries of Example 3 and Example 4 showed a high capacity retention rate even after repeating 200 charge and discharge cycles and had excellent cycle stability.

[0242] FIG. 12 shows, by additional experiments, that during the production of the positive electrode of Example 3, the sulfur loading amounts were 1.5 mg / cm 2 、3.5 mg / cm 2 、5.0 mg / cm 2The results are shown below after changing the settings, adjusting the E / S ratio to 4.0 μL / mg, and performing 100 charge-discharge cycles under a 0.1C rate, followed by measurement of the discharge capacity. As shown in Figure 12, it was confirmed that the lithium-sulfur battery performed well even under harsh conditions when using the FeNC-EEB-1 carbon composite.

[0243] Based on these results, it was confirmed that catalysts incorporating -SO2 / -S EEB sites formed by sulfur doping around transition metal-containing catalysts exhibit excellent effects on high capacity, cycle stability, discharge capacity ratio, and low polarity in lithium-sulfur batteries.

[0244] In particular, it was confirmed that carbon composites with EEB sites having a low -SO2 / -S ratio were more effective in improving the performance of lithium-sulfur batteries than carbon composites with EEB sites having a high -SO2 / -S ratio. Further experiments confirmed that this is because the -S structure around the catalyst is more effective than the -SO2 structure in regulating the binding energy of LiPS and the energy barrier of the conversion reaction between Li2S4 and Li2S.

[0245] [Battery manufacturing] Example 5 Manufacturing of positive electrodes Carbon nanotubes (CNTs, BET specific surface area 150-350 m²) 2 A positive electrode active material was obtained by supporting 75 wt% sulfur (sulfur powder, manufactured by Sigma-Aldrich) on 25 wt% of (g).

[0246] Using NMP (N-methyl-2-pyrrolidone) solvent, the cathode active material prepared above and carbon nanotubes (CNT, BET specific surface area 150-350 m) as conductive materials are used. 2 A cathode slurry was prepared by mixing ( / g) with the carbon composite (FeNC-EEB-1) from Example 1 prepared above as an additive, and PVDF (polyvinylidene fluoride) as a binder, in a weight ratio of 90:2.5:2.5:5.

[0247] The manufactured positive electrode slurry was coated onto carbon-coated aluminum foil and then dried at 60°C for 8 hours. After that, the electrode was pressurized and cut into coin shapes to produce the positive electrode.

[0248] Battery manufacturing The battery was manufactured in the same manner as in Example 3, except that the positive electrode manufactured as described above was used.

[0249] The loading amount of sulfur in the positive electrode is 3.5 mg / cm³. 2 That was the case.

[0250] Comparative Example 3 A battery was manufactured in the same manner as in Example 5, except that the positive electrode slurry was produced by mixing the positive electrode active material, the conductive material, and the binder in a weight ratio of 90:5:5, without mixing in the carbon composite (FeNC-EEB-1).

[0251] The loading amount of sulfur in the positive electrode is 3.5 mg / cm³. 2 That was the case.

[0252] [Evaluation of battery performance] To evaluate the charge and discharge performance of the batteries in Example 5 and Comparative Example 3, the current density at a 0.1C rate and the voltage at 1.7~2.6V (vs.Li / Li) were measured for the batteries in Example 5 and Comparative Example 3. + The charge and discharge performance was evaluated within the voltage range, and the results are shown in Figure 13.

[0253] Figure 13 shows the initial voltage characteristics of batteries in Example 5 and Comparative Example 3 at a 0.1C rate. This confirms that in Example 5, using a carbon composite (FeNC-EEB-1) as the positive electrode additive not only improves the initial discharge capacity but also enhances the battery's reactivity.

[0254] This is presumably because the carbon composite according to the present invention has the effect of a catalytic additive that adsorbs lithium polysulfide and acts as a catalyst to promote its conversion reaction, compared to ordinary conductive materials used in positive electrodes. However, the effects of the present invention are not limited to this.

Claims

1. A porous carbon material doped with at least one sulfur, A catalyst comprising at least one transition metal, Includes, The catalyst is located on at least one of the outer surface and the inner surface of the pores of the porous carbon material doped with at least one sulfur, so that the at least one sulfur doped in the porous carbon material forms electron-exchangeable bonding (EEB) sites that exchange electrons with one or more transition metals. The at least one sulfur is doped in the form of a sulfur atom or a sulfur compound, The porous carbon material doped with at least one sulfur is a carbon composite having at least one of the structures -C-S-C- and -C-SOx-C- (0.1 ≤ x ≤ 4) within its structure.

2. The carbon composite according to claim 1, wherein the nearest neighbor interatomic distance between the transition metal contained in the catalyst and at least one sulfur doped into the porous carbon material is 10 nm or less.

3. The carbon composite according to claim 1, wherein the nearest neighbor interatomic distance between the transition metal contained in the catalyst and at least one sulfur doped into the porous carbon material is 2 nm or less.

4. The carbon composite is 200 m ２ The carbon composite according to claim 1, having a BET specific surface area of ​​1g or more.

5. The carbon composite according to claim 1, wherein the catalyst further comprises the transition metal and at least one nonmetallic element that forms a ligand with the transition metal.

6. The carbon composite according to claim 1, wherein the catalyst further comprises the transition metal, at least one nonmetallic element that forms a ligand with the transition metal, and an organic support.

7. The catalyst includes a single-atom catalyst containing one or more transition metals, The carbon composite according to claim 1, wherein one or more transition metals are dispersed within the carbon composite at a single-atom scale.

8. The carbon composite according to claim 1, wherein no metallic bonds are included between the two or more transition metals contained in the catalyst.

9. The catalyst comprises particles containing one or more transition metals, The average diameter of the aforementioned particles (D ５０ The carbon composite according to claim 1, wherein the diameter of the single atom constituting the transition metal is 1 to 30 nm.

10. The catalyst comprises particles containing one or more transition metals, The average diameter of the aforementioned particles (D ５０ The carbon composite according to claim 1, wherein the diameter of the single atom constituting the transition metal is 1 to 5 times the diameter of the single atom constituting the transition metal.

11. The carbon composite according to claim 1, wherein the transition metal is zinc (Zn), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), rubidium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), cadmium (Cd), lanthanum (La), hafnium (Hf), tantalum (Ta), tungsten (W), osmium (Os), iridium (Ir), cerium (Ce), galadium (Gd), scandium (Sc), titanium (Ti), gallium (Ga), indium (In), or two or more of these.

12. The carbon composite according to claim 1, wherein the transition metal includes iron (Fe).

13. The transition metal includes iron (Fe), The diameter of the iron contained in the carbon composite (D ５０ The carbon composite according to claim 1, wherein the n is 0.3 nm to 5 nm.

14. The carbon composite according to claim 1, wherein the molar ratio of sulfur doped into the porous carbon material to one or more transition metals contained in the catalyst is 0.5 to 8.

15. The porous carbon material doped with at least one sulfur contains in its structure at least one of the following structures: a first structure according to formula 1 and a second structure according to formula 2. The ratio of the first structure to the second structure is the molar ratio of the first structure to the second structure, and is 1 or less. [Formula 1] -C-SO ２ -C- "Formula 2" -C-S-C- The carbon composite according to claim 1.

16. The carbon composite according to claim 15, wherein the molar ratio of the first structure to the second structure is 0.1 to 0.

7.

17. When N (nano) is the number of pores with a diameter of less than 10 nm among all the pores of the carbon composite, and N (macro) is the number of pores with a diameter of 10 nm or more, The carbon composite according to claim 1, wherein the ratio of N(macro) to N(nano) [N(macro) / N(nano)] is 1 or more.

18. The Raman peak intensity ratio (I) of the porous carbon material Ｇ / I Ｄ The carbon composite according to claim 1, wherein the ratio is 1 or less.

19. A method for producing a carbon composite according to claim 1, (S1) Doping a porous carbon material with at least one sulfur to obtain a porous carbon material doped with at least one sulfur element, (S2) After impregnating the transition metal-containing precursor solution with the result of step (S1), the solvent is removed. Includes, The step in (S1) above includes a step of heat-treating the sulfur-doped precursor and the porous carbon material at a temperature of 800°C to 1,000°C while they are in contact, The at least one sulfur is doped in the form of a sulfur atom or a sulfur compound, A method for producing a carbon composite, wherein the porous carbon material doped with at least one sulfur contains at least one of the structures -C-S-C- and -C-SOx-C- (0.1 ≤ x ≤ 4) within its structure.

20. The sulfur-doped precursor is dibenzyl disulfide (DBDS), sodium metabisulfite (Na ２ S ２ O ５ ), sodium pyrosulfate (Na ２ S ２ O ７ ), sodium thiosulfate (Na ２ S ２ O ３ ), thiourea (CH ４ N ２ S), sodium sulfide (Na ２ S), potassium thiocyanate (KSCN), benzyl mercaptan (C ７ H ８ S), benzothiophene (C ８ H ６ S), dibenzothiophene (C １２ H ８ S), or a mixture thereof, the method for producing a carbon composite according to claim 19.

21. The transition metal-containing precursor solution in step (S2) is Organic solvents and Precursor compounds of nonmetallic elements, A method for producing a carbon composite according to claim 19, comprising a transition metal precursor compound.

22. A positive electrode active material for a lithium sulfur battery, A carbon composite according to any one of claims 1 to 18, and a sulfur-based compound, The sulfur-based compound is a lithium sulfide (Li₂S), lithium polysulfide (Li₂Sx, 2≦x≦8), a disulfide compound, or a mixture of two or more of these, which is the positive electrode active material.

23. A positive electrode comprising the positive electrode active material described in claim 22.

24. The system includes a positive electrode, a negative electrode, a separation membrane interposed between the positive electrode and the negative electrode, and an electrolyte. A lithium sulfur battery wherein the positive electrode is the positive electrode described in claim 23.

25. A positive electrode for a lithium-sulfur battery, A positive electrode active material containing a sulfur-based compound and a carbon composite according to any one of claims 1 to 18, The sulfur-based compound is lithium sulfide (Li₂S), lithium polysulfide (Li₂Sx, 2≦x≦8), a disulfide compound, or a mixture of two or more of these, in the positive electrode.

26. The system includes a positive electrode, a negative electrode, a separation membrane interposed between the positive electrode and the negative electrode, and an electrolyte. A lithium sulfur battery wherein the positive electrode is the positive electrode described in claim 25.

Images